Ash handling and treatment in solid fuel burners

ABSTRACT

A solid fuel gasifier includes first wall structure ( 12 ) defining a gasification chamber ( 14 ) and means ( 50, 52 ) to collect particulate solid residue from gasification in the gasification chamber. Second wall structure ( 16 ) defines a gas combustion chamber ( 17 ) and means ( 19 ) is arranged for admitting a flow of hot gases from the gasification chamber to the gas combustion chamber as combustion takes place. Also provided is means ( 178, 170 ) to conduct hot gases from the gasification chamber and/or gas combustion chamber into thermal contact with said collected particulate solid residue, for facilitating post-combustion and/or post-reduction of the solid residue. Also disclosed are an agitator bed ( 52, 182 ) for fine particulate material, and a method of gasification of solid fuel.

FIELD OF THE INVENTION

[0001] This invention relates generally to solid fuel burners and hasparticular, though not exclusive, application to a solid fuel burner ofthe type commonly referred to as a gasifier or gasifier combustor.

BACKGROUND ART

[0002] A gasifier generally includes a primary combustion chamber intowhich solid fuel is loaded on to a grate structure. The fuel is firstdried and gasified on the grate structure in a controlled primarycombustion. The resultant gas is then transferred into a secondarycombustion chamber, which may conveniently be a cycloburner, forsecondary combustion to produce a high temperature relatively clean fluegas able to be used for a variety of purposes, eg. power generation orheating. There is a small residue of inorganic matter.

[0003] A gasifier of the general type to which the present inventionrelates is disclosed, for example, in U.S. Pat. No. 4,716,842, and thetechnology generally is of particular interest in waste recycling,especially with an emphasis on so-called “green power” generation.Specific solid fuels that may conveniently be gasified in this wayinclude biological waste, agricultural biproducts, waste and biomass.

[0004] An objective of the present invention is to improve theprocessing of the solid residue recovered from the gasification process.

SUMMARY OF THE INVENTION

[0005] In a first aspect of the invention it has been appreciated thatone way of achieving the objective is to bring the residue into thermalcontact with off-gases recovered from the gasifier or secondarycombustion chamber, preferably the latter, whereby to achieve anadvantageous degree of post-combustion or post-reduction of the solidresidue.

[0006] In accordance with the first aspect of the invention, therefore,there is provided a solid fuel gasifier including:

[0007] first wall structure defining a gasification chamber;

[0008] means to collect particulate solid residue from gasification inthe gasification chamber;

[0009] second wall structure defining a gas combustion chamber;

[0010] means arranged for admitting a flow of hot gases from saidgasification chamber to said gas combustion chamber as combustion takesplace; and

[0011] means to conduct hot gases from said gasification and/or gascombustion chamber into thermal contact with said collected particulatesolid residue, for facilitating post-combustion and/or post-reduction ofthe solid residue.

[0012] In the first aspect of the invention, there is further provided asolid fuel gasifier including:

[0013] first wall structure defining a gasification chamber, said wallstructure including a floor on which particulate solid residue isaccumulated during gasification in the chamber;

[0014] second wall structure defining a gas combustion chamber;

[0015] means arranged for admitting a flow of hot gases from saidgasification chamber to said gas combustion chamber as combustion takesplace; and

[0016] means to conduct hot gases from said gasification and/or gascombustion chamber through said floor, for superheating the floor andfacilitating post-combustion and/or post-reduction of said accumulatedsolid residue thereon.

[0017] Preferably, said means to conduct the hot gases through the floorcomprises multiple passages, eg. pipes, extending through or adjacent tothe floor structure.

[0018] In a second aspect, the invention provides an agitator bed forfine particulate material, including:

[0019] a base surface for supporting the particulate material;

[0020] an array of agitator elements arranged adjacent to and dispersedover the base surface; and

[0021] means to reciprocate or otherwise move said agitator elementsthrough said material on said base surface for agitating the material toencourage post-combustion and/or post reduction, and for effecting a netconveyance of the material in a predetermined direction;

[0022] wherein said agitator elements are shaped to present varyingsurface profiles to said material on said base surface that facilitatesaid net conveyance of the material in said predetermined direction.

[0023] Preferably, each of the agitator elements includes anasymmetrical triangular pyramidal base section which presents astreamlined face in one direction and a relatively more abutting face inthe other. Advantageously, each agitator element further includes anenlarged head section atop the base section to further assist in partingthe upper layers of the accumulated particulate material.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The invention will now be further described, by way of exampleonly, with reference to accompanying drawings, in which:

[0025]FIG. 1 is a diagrammatic vertical longitudinal section of a solidstate gasifier incorporating an embodiment of both aspects of theinvention;

[0026]FIG. 2 is a diagrammatic plan view of the internal floor structureby which hot gases from the secondary or gas combustion chamber arerecycled into thermal contact with solids residue in the primary orgasification chamber;

[0027]FIG. 3 is a view on the line 3-3 in FIG. 2;

[0028]FIG. 4 is a plan view of the agitator bed on the floor; and

[0029]FIGS. 5, 6 and 7 are various views of an agitator element.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0030] The solid fuel gasifier 10 of FIG. 1 (which includes a figure ofa man 11 to provide a dimensional context), includes an outer housing 12about a primary combustion or gasification chamber 14 extending from afuel delivery auger 9 towards a separately walled cycloburner 16 thatdefines a secondary gas combustion chamber 17. A grate structure 20includes a preheating grate 22 adjacent the delivery end of auger 9,and, downstream in the overall direction of flow of the solid fuel, agasifier grate 24. The two grates 22, 24 each include stepped pairs offixed 30 and reciprocating 32 grate segments and are linked by a nearvertical grate 40 with multiple angled and controllable openings 42 foradmission of combustion air from below the grate structure into the fuelload above.

[0031] In general, solid fuel delivered via auger 9 accumulates as adeep load or burden 70 on the grate structure while being dried andpreheated on grate 22 and gasified above grate 24. Combustible gas(syngas) is drawn through a transverse slot port 19 into chamber 17,from one end 15 of which is recovered combusted off-gas, flue gas orsyngas useable for subsequent heating or power generating purposes.Inorganic solid residue or ash that falls over the downstream end ofgrate 24 is directed by a baffle device 50 onto an ash grate 52 arrangedon the floor 13 of the housing. The ash is gradually agitated and movedalong grate 52 while remaining carbon in the ash is oxidised to CO₂ andCO, for transverse removal and recovery by conveyor 54. Thispost-combustion of the remaining carbon is facilitated by heating floor13.

[0032] An overhead water-cooled refractory lining 56 is suspended fromthe roof 11 of housing 10 and merges into the wall structure ofcycloburner 16. Lining 56 also defines one edge of slot port 19 throughwhich combustible gases pass from the primary chamber 14 to thesecondary chamber 17. Roof 11 supports an emergency exhaust stack 58.

[0033] Floor 13 of primary or gasification chamber 14 is heated by meansof an internal array 170 (FIG. 2) of parallel ducts 171 extendingbetween transverse tubular manifolds 172, 173 respectively at a positiongenerally below cycloburner 16 and at the front end of housing 12 belowfuel delivery auger 9. As seen in FIG. 3, transverse manifold 172 is atthe feed or delivery end of this array 170 and is fed during operationof the burner with the off-gas from secondary or gas combustion chamber17. This gas is recovered from chamber 17 via a vortex cone 174 (toseparate out particulate content) fitted to the end wall of burner 16,and an inclined and insulated hot gas conduit 178. A substantiallycylindrical extension 179 at the apex of vortex cone 174 links toconduit 178 and incorporates an eye glass 175.

[0034] Floor gas outlet manifold 173 is linked to a fan (not shown) inwhich the air is mixed with cool ambient air and/or flue gas to preventfan overheat. The air mixture may be variously extracted for furtheruse, or wholly or in part recycled to primary combustion or gasificationchamber 14, for example via the grates 22, 24. In this way, whereappropriate, an organic-contaminated stream from the cycloburner may bereinjected to the gasifier chamber to allow further gasification of thestill contained carbonaceous material.

[0035] The recycled hot gases in the floor 13 are effective to superheatthe floor and thereby superheat the solid residue which has dropped ontoand accumulated on the floor. In this way, the residue, which istypically a fine particulate ash, is further treated by post-combustionor post-reduction wholly or at least in part.

[0036] In an advantageous form of the invention, a grate mechanism 52 isprovided for agitating the ash on floor 13 to facilitate thepost-combustion or post-reduction, while simultaneously slowly butprogressively moving the material along the floor 13 to recoveryconveyor 54.

[0037] Mechanism 52 essentially comprises a reciprocable grid on floor13 that consists of multiple agitator elements 182 arranged in a diamondarray on several longitudinally extending mounting bars 184. Bars 184are fixed together by cross-bars 186, 187 to form a framework that isreciprocated longitudinally of floor 13 by an actuator 188 located justforwardly of housing 12.

[0038] Agitator elements 182 are of similar form and are designed topart and stir the ash material when moved in the direction away fromconveyor 54 but tend to move the ash material towards the conveyor whenmoved in the other direction. This is well achieved by the configurationdepicted in FIGS. 5 to 7. Each agitator element 182 has a base section190 of a symmetrical triangular pyramidal form, presenting a parting orstreamlined face 192 when the element is moved away from conveyor 54,but presenting a vertically flat triangular face 194 towards theconveyor 54. Parting or streamlined face 192 preferably has lateraledges 50-75° (preferably about 65°) apart and a central inclination of20-40° (preferably about 25°). A winged head section 195, made in twoparts 196, 197 bolted together, further assists in combing through andagitating the upper layers of the ash layer.

[0039] In some cases, it has been found more appropriate for the ashmaterial to be moved to a recovery conveyor at the opposite end of thefurnace, ie. at the right in FIG. 1. In this event, the agitatorelements need to be reversed to an orientation opposite to that shown inFIG. 1 ie. with face 194 facing to the right. This reversed direction offlow can, in some cases, be advantageous, for example by increasing theoverall residence time of the ash on floor 13, thereby enhancingpost-reduction and/or post combustion.

[0040] In a further modification, control of the process ofpost-combustion of the ash on floor 13 is enhanced by a facility to coolor limit the maximum temperature of the ash. For example, provision maybe included to spray water onto the ash, and/or floor 13 may include anadditional network of passages for cooling fluid, and/or water vapour orair may be selectively mixed into the gas flow of duct array 170. Thelatter may be achieved by recycling or mixing in vapour fromgasification chamber 14. In another modification, air with or withoutadded water vapour may be injected into the ash from locations on floor13, eg. adjacent agitator elements 182 or via ducts within elements 182.

1. A solid fuel gasifier including: first wall structure defining agasification chamber; means to collect particulate solid residue fromgasification in the gasification chamber; second wall structure defininga gas combustion chamber; means arranged for admitting a flow of hotgases from said gasification chamber to said gas combustion chamber ascombustion takes place; and means to conduct hot gases from saidgasification chamber and/or gas combustion chamber into thermal contactwith said collected particulate solid residue, for facilitatingpost-combustion and/or post-reduction of the solid residue.
 2. A solidfuel gasifier according to claim 1 wherein said means to collectparticulate solid residue includes a floor of said wall structure, onwhich floor said particulate solid residue is accumulated duringgasification in the chamber.
 3. A solid fuel gasifier according to claim2 wherein said gasification chamber further contains grate means onwhich solid fuel accumulates for gasification, and wherein said means tocollect particulate solid residue further includes baffle means in saidgasification chamber to direct to said floor particulate solid residuethat falls from said grate means.
 4. A solid fuel gasifier according toclaim 1, 2 or 3 wherein said means to conduct the hot gases through thefloor comprises multiple passages extending through or adjacent to thefloor structure.
 5. A solid fuel gasifier according to any one of claims1 to 4, wherein said second wall structure is a cycloburner and saidmeans to conduct hot gases includes conduit means to deliver off-gasfrom said gas combustion chamber into thermal contact with the collectedparticulate solid residue.
 6. A solid fuel gasifier according to any oneof claims 1 to 5, further including an agitator bed for said particulatesolid residue, including: a base surface for supporting the particulatesolid residue; an array of agitator elements arranged adjacent to anddispersed over the base surface; and means to reciprocate or otherwisemove said agitator elements through said solid residue on said basesurface for agitating the solid residue to encourage post-combustionand/or post reduction, and for effecting a net conveyance of the solidresidue in a predetermined direction; wherein said agitator elements areshaped to present varying surface profiles to said solid residue on saidbase surface that facilitate said net conveyance of the solid residue insaid predetermined direction.
 7. A solid fuel gasifier according toclaim 6 wherein said base surface is a floor of said gasificationchamber.
 8. A solid fuel gasifier according to claim 6 or 7, whereineach of said agitator elements includes an asymmetrical triangularpyramidal base section which presents a streamlined face in onedirection and a relatively more abutting face in the other.
 9. A solidfuel gasifier according to claim 6, 7 or 8, wherein each of saidagitator elements includes an enlarged head section atop the basesection to further assist in parting the upper layers of the accumulatedparticulate material.
 10. A solid fuel gasifier according to any one ofclaims 6 to 9 wherein said agitator elements are mounted on areciprocable grid.
 11. A solid fuel gasifier according to any one ofclaims 1 to 10, further including means to deliver said gases, aftersaid thermal contact with said collected particulate solid residue, intosaid gasification chamber.
 12. A solid fuel gasifier according to claim11, wherein said gasification chamber further contains grate means onwhich solid fuel accumulates for gasification, and said delivery meansis arranged to deliver said gases into said gasification chamber viasaid grate means.
 13. A solid fuel gasifier according to any one ofclaims 1 to 12, further including means to apply a cooling medium tocool or limit the maximum temperature of said collected particulatesolid residue, for enhanced control of said post-combustion and/orpost-reduction thereof.
 14. An agitator bed for fine particulatematerial, including: a base surface for supporting the particulatematerial; an array of agitator elements arranged adjacent to anddispersed over the base surface; and means to reciprocate or otherwisemove said agitator elements through said material on said base surfacefor agitating the material to encourage post-combustion and/or postreduction, and for effecting a net conveyance of the material in apredetermined direction; wherein said agitator elements are shaped topresent varying surface profiles to said material on said base surfacethat facilitate said net conveyance of the material in saidpredetermined direction.
 15. A solid fuel gasifier according to claim14, wherein each of said agitator elements includes an asymmetricaltriangular pyramidal base section which presents a streamlined face inone direction and a relatively more abutting face in the other.
 16. Asolid fuel gasifier according to claim 14 or 15, wherein each of saidagitator elements includes an enlarged head section atop the basesection to further assist in parting the upper layers of the accumulatedparticulate material.
 17. A solid fuel gasifier according to any one ofclaims 14, 15 or 16 wherein said agitator elements are mounted on areciprocable grid.
 18. A method of gasification of solid fuel,including: gasifying the solid fuel in a gasification chamber; admittinghot gases from said gasification chamber into a gas combustion chamber;combusting said hot gases in said gas combustion chamber; collectingparticulate solid residue from said gasification chamber; and conductinghot gases from said gasification chamber and/or gas combustion chamberinto thermal contact with said collected particulate solid residue, forfacilitating post-combustion and/or post-reduction of the solid residue.19. A method according to claim 18, further including delivering saidgases, after said thermal contact with said collected particulate solidresidue, into said gasification chamber.
 20. A method according to claim19, wherein said delivery of said gases into the gasification chamber isvia grate means on which solid fuel accumulates for gasification.
 21. Amethod according to claim 18, 19 or 20 further including applying acooling medium to cool or limit the maximum temperature of saidcollected particulate solid residue, for enhanced control of saidpost-combustion and/or post-reduction thereof.